CN117452743A

CN117452743A - Optical device

Info

Publication number: CN117452743A
Application number: CN202311415252.6A
Authority: CN
Inventors: 中村和树; 稻田安寿
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2019-04-26
Filing date: 2020-02-07
Publication date: 2024-01-26
Also published as: US20210405289A1; US11953726B2; WO2020217646A1; CN113474721B; JP2024026881A; JPWO2020217646A1; JP7429908B2; CN113474721A

Abstract

The optical device is provided with: a 1 st waveguide extending in the 1 st direction; and a 2 nd waveguide extending in the 1 st direction; the 2 nd waveguide includes: a 1 st mirror having a 1 st reflecting surface; a 2 nd mirror having a 2 nd reflecting surface facing the 1 st reflecting surface; and an optical waveguide layer between the 1 st mirror and the 2 nd mirror; at least one of the 1 st waveguide and the 2 nd waveguide has 1 or more gratings in a part of a region where the 1 st mirror, the 2 nd mirror, and the 1 st waveguide overlap when viewed from a direction perpendicular to the 1 st reflection surface; the 1 or more gratings are spaced apart from the end of the 1 st mirror or the 2 nd mirror in the overlapping region by a distance longer than at least one of the thickness of the 1 st mirror and the thickness of the 2 nd mirror in the 1 st direction.

Description

Optical device

The present application is a divisional application of patent application of the invention having the application number 202080016865.0 and the name of "optical device" and having the application date 2020, 2 and 7.

Technical Field

The present invention relates to optical devices.

Background

Conventionally, various apparatuses capable of scanning (scan) a space with light have been proposed.

Patent document 1 discloses a structure in which scanning of passing light can be performed using a driving device that rotates a mirror.

Patent document 2 discloses an optical phased array having a plurality of nanophotonic antenna elements arranged in two dimensions. Each antenna element is optically coupled to a variable optical delay line (i.e., phase shifter). In this optical phased array, a coherent light beam is guided to each antenna element through a waveguide, and the phase of the light beam is shifted by a phase shifter. Thereby, the amplitude distribution of the far-field radiation pattern can be changed.

Patent document 3 discloses an optical deflection element including: an optical waveguide having an optical waveguide layer for guiding light internally and 1 st distributed Bragg mirrors formed on upper and lower surfaces of the optical waveguide layer; a light entrance port for making light incident into the optical waveguide; and a light exit port formed on a surface of the optical waveguide so as to emit light that enters from the light entrance port and is guided in the optical waveguide.

Patent document 4 discloses an optical scanning device provided with a 1 st waveguide that propagates light by total reflection and a 2 nd waveguide that propagates light between 2 multilayer reflective films. The 1 st waveguide and the 2 nd waveguide are connected.

Prior art literature

Patent literature

Patent document 1: international publication No. 2013/168864

Patent document 2: japanese patent application laid-open No. 2016-508235

Patent document 3: japanese patent application laid-open No. 2013-16591

Patent document 4: international publication No. 2018/061514

Disclosure of Invention

Problems to be solved by the invention

An object of the present invention is to provide a novel optical device capable of realizing optical coupling between waveguides with a relatively simple structure.

Means for solving the problems

An optical device according to an aspect of the present invention includes: : a 1 st waveguide extending in the 1 st direction; and a 2 nd waveguide extending in the 1 st direction; the 2 nd waveguide includes: a 1 st mirror having a 1 st reflecting surface; a 2 nd mirror having a 2 nd reflecting surface facing the 1 st reflecting surface; and an optical waveguide layer between the 1 st mirror and the 2 nd mirror; at least one of the 1 st waveguide and the 2 nd waveguide has 1 or more gratings in a part of a region where the 1 st mirror, the 2 nd mirror, and the 1 st waveguide overlap when viewed from a direction perpendicular to the 1 st reflection surface; the 1 or more gratings are spaced apart from the end of the 1 st mirror or the 2 nd mirror in the overlapping region by a distance longer than at least one of the thickness of the 1 st mirror and the thickness of the 2 nd mirror in the 1 st direction.

The inclusion or specific aspects of the present invention may also be implemented by an apparatus, system, method, or any combination thereof.

Effects of the invention

According to an aspect of the present invention, optical coupling between waveguides can be achieved with a relatively simple structure.

Drawings

Fig. 1 is a perspective view schematically showing an example of an optical scanning apparatus.

Fig. 2 is a diagram schematically showing an example of a cross-sectional structure of one waveguide element and propagating light.

Fig. 3A is a view showing a cross section of a waveguide array that emits light in a direction perpendicular to an emission surface of the waveguide array.

Fig. 3B is a view showing a cross section of the waveguide array which emits light in a direction different from the direction perpendicular to the emission surface of the waveguide array.

Fig. 4 is a perspective view schematically showing an example of a waveguide array in a three-dimensional space.

Fig. 5 is a schematic view of the waveguide array and the phase shifter array as viewed from the normal direction (Z direction) of the light emitting surface.

Fig. 6 is a diagram schematically showing an example of an optical device in which the shape of the end portion of the 1 st mirror is changed by machining.

Fig. 7 is a graph showing a relationship between a change in thickness of the optical waveguide layer and a diffusion angle of light emitted from the 1 st mirror.

Fig. 8A is a diagram schematically showing an optical apparatus according to an exemplary embodiment of the present invention.

Fig. 8B is a schematic diagram of the connection of the total reflection waveguide and the slow optical waveguide shown in fig. 8A as viewed from the Z direction.

Fig. 9 is a diagram schematically showing an example of an optical device having a longer distance from the interface to the grating.

Fig. 10A is a diagram schematically showing a modification 1 of the optical device shown in fig. 8A.

Fig. 10B is a diagram schematically showing a modification 2 of the optical device shown in fig. 8A.

Fig. 10C is a diagram schematically showing a modification 3 of the optical device shown in fig. 8A.

Fig. 11A is a diagram schematically showing a 4 th modification of the optical device shown in fig. 8A.

Fig. 11B is a diagram schematically showing a 5 th modification of the optical device shown in fig. 8A.

Fig. 12 is a diagram showing a configuration example of an optical scanning device in which elements such as a beam splitter, a waveguide array, a phase shifter array, and a light source are integrated on a circuit board.

Fig. 13 is a schematic diagram showing a situation in which a two-dimensional scanning is performed by irradiating a beam of laser light or the like from an optical scanning device to a distant place.

Fig. 14 is a block diagram showing a configuration example of a LiDAR system capable of generating a range image.

Detailed Description

In the present specification, the term "at least one of refractive index, thickness, and wavelength" means at least one selected from the group consisting of refractive index of an optical waveguide layer, thickness of an optical waveguide layer, and wavelength input to an optical waveguide layer. In order to change the light emission direction, any one of the refractive index, thickness, and wavelength may be individually controlled. Alternatively, any two or all of these 3 may be controlled to change the light emission direction. Instead of or in addition to controlling the refractive index or thickness, the wavelength of light input to the optical waveguide layer may be controlled.

The above basic principle can be applied not only to the use of emitted light but also to the use of received light signals. By changing at least one of the refractive index, the thickness, and the wavelength, the direction of the receivable light can be changed one-dimensionally. Further, if the phase difference of the light is changed by a plurality of phase shifters connected to a plurality of waveguide elements arranged in one direction, the direction of the receivable light can be changed two-dimensionally.

The optical scanning device and the optical receiving device of the present invention can be used as an antenna of a light detection system such as a LiDAR (Light Detection and Ranging) system. The LiDAR system uses electromagnetic waves (visible light, infrared light, or ultraviolet light) having a short wavelength as compared with radar systems using radio waves such as millimeter waves, and thus can detect the distance distribution of an object with a high resolution. Such LiDAR systems are mounted in, for example, automobiles and UAVs (Unmannned beer) _i a mobile object such as al Vehicle, so-called unmanned aerial Vehicle), AGV (Automated Guided Vehicle), or the like can be used as one of the collision avoidance technologies. In this specification, an optical scanning device and an optical receiving device are collectively referred to as an "optical device". In addition, as for an apparatus used in an optical scanning apparatus or an optical receiving apparatus, there is also a case called an "optical apparatus".

< structural example of optical scanning device >

The configuration of an optical scanning device that performs two-dimensional scanning will be described below as an example. However, the above detailed description may be omitted. For example, a detailed description of known matters may be omitted, and a description of substantially the same structure may be repeated. This is to avoid that the following description becomes unnecessarily lengthy and easy to understand by a person skilled in the art. The drawings and the following description are provided to enable those skilled in the art to fully understand the present invention, and are not intended to limit the subject matter recited in the claims. In the following description, the same or similar constituent elements are given the same reference numerals.

In the present invention, "light" means electromagnetic waves including not only visible light (wavelength of about 400nm to about 700 nm) but also ultraviolet light (wavelength of about 10nm to about 400 nm) and infrared light (wavelength of about 700nm to about 1 mm). In the present specification, ultraviolet rays may be referred to as "ultraviolet light" and infrared rays may be referred to as "infrared light".

In the present invention, the term "scanning" based on light means changing the direction of light. "one-dimensional scanning" means that the direction of light is linearly changed along a direction intersecting with the direction. "two-dimensional scanning" means changing the direction of light two-dimensionally along a plane intersecting the direction.

Fig. 1 is a perspective view schematically showing an example of an optical scanning apparatus 100 of the embodiment. The optical scanning device 100 is provided with a waveguide array including a plurality of waveguide elements 10. The plurality of waveguide elements 10 each have a shape extending in the 1 st direction (X direction in fig. 1). The plurality of waveguide elements 10 are regularly arranged in the 2 nd direction (Y direction in fig. 1) intersecting the 1 st direction. The plurality of waveguide elements 10 emit light in a 3 rd direction D3 intersecting a virtual plane parallel to the 1 st and 2 nd directions while allowing the light to propagate in the 1 st direction. In the present invention, the 1 st direction (X direction) is orthogonal to the 2 nd direction (Y direction), but the two directions may not be orthogonal. In the present invention, the plurality of waveguide elements 10 are arranged at equal intervals in the Y direction, but are not necessarily arranged at equal intervals.

The orientation of the structure shown in the drawings of the present application is set in consideration of the description and is not limited to the orientation at the time of implementation. The shape and size of the whole or a part of the structure shown in the drawings are not limited to the actual shape and size.

The plurality of waveguide elements 10 each include a 1 st mirror 30 and a 2 nd mirror 40 (hereinafter, each will be simply referred to as a "mirror") facing each other, and an optical waveguide layer 20 located between the mirrors 30 and 40. The mirror 30 and the mirror 40 each have a reflection surface intersecting the 3 rd direction D3 at an interface with the optical waveguide layer 20. The mirrors 30 and 40 and the optical waveguide layer 20 have shapes extending in the 1 st direction (X direction).

As will be described later, the 1 st mirrors 30 of the waveguide elements 10 may be integrally formed mirrors. The 2 nd mirrors 40 of the waveguide elements 10 may be integrally formed mirrors. Further, the plurality of optical waveguide layers 20 of the plurality of waveguide elements 10 may be a plurality of portions of an integrally formed optical waveguide layer. At least (1) each 1 st mirror 30 is formed separately from the other 1 st mirrors 30, or (2) each 2 nd mirror 40 is formed separately from the other 2 nd mirrors 40, or (3) each optical waveguide layer 20 is formed separately from the other optical waveguide layers 20, whereby a plurality of waveguides can be formed. "divided constitution" includes not only physically disposing a space but also separating by sandwiching a material having a different refractive index.

The reflective surface of the 1 st mirror 30 and the reflective surface of the 2 nd mirror 40 are opposed substantially in parallel. Of the two mirrors 30 and 40, at least the 1 st mirror 30 has a property of transmitting a part of light propagating through the optical waveguide layer 20. In other words, the 1 st mirror 30 has a higher light transmittance than the 2 nd mirror 40 for the light. Therefore, a part of the light propagating through the optical waveguide layer 20 is emitted from the 1 st mirror 30 to the outside. Such mirrors 30 and 40 may be, for example, multilayer film mirrors formed of dielectric-based multilayer films (also referred to as "multilayer reflective films").

By controlling the phase of the light input to each waveguide element 10 and further simultaneously changing the refractive index or thickness of the optical waveguide layer 20 of each waveguide element 10 or the wavelength of the light input to the optical waveguide layer 20, a two-dimensional scanning by light can be realized.

The present inventors analyzed the principle of operation of the waveguide element 10 in order to realize such two-dimensional scanning. Based on the result, by synchronously driving the plurality of waveguide elements 10, the light-based two-dimensional scanning is successfully achieved.

As shown in fig. 1, if light is input to each waveguide element 10, the light is emitted from the emission surface of each waveguide element 10. The exit face is located on the opposite side of the reflective face of mirror 1, mirror 30. The direction D3 of the emitted light depends on the refractive index and thickness of the optical waveguide layer and the wavelength of the light. In the present invention, at least one of the refractive index, thickness, and wavelength of each optical waveguide layer is synchronously controlled so that the light emitted from each waveguide element 10 is in substantially the same direction. This allows the component in the X direction of the wave number vector of the light emitted from the plurality of waveguide elements 10 to be changed. In other words, the direction D3 of the emitted light can be changed along the direction 101 shown in fig. 1.

Further, since the light emitted from the plurality of waveguide elements 10 is directed in the same direction, the emitted light interferes with each other. By controlling the phase of the light emitted from each waveguide element 10, the direction in which the light intensifies each other by interference can be changed. For example, in the case where a plurality of waveguide elements 10 of the same size are arranged at equal intervals in the Y direction, light whose phases are each different by a certain amount is input to the plurality of waveguide elements 10. By changing the phase difference, the component in the Y direction of the wave number vector of the emitted light can be changed. In other words, by changing the phase differences of the lights introduced into the plurality of waveguide elements 10, the direction D3 in which the outgoing lights strengthen each other by interference can be changed along the direction 102 shown in fig. 1. Thereby, two-dimensional scanning by light can be realized.

The principle of operation of the optical scanning device 100 is described below.

< principle of action of waveguide element >

Fig. 2 is a diagram schematically showing an example of a cross-sectional structure and propagating light of one waveguide element 10. In fig. 2, the direction perpendicular to the X direction and the Y direction shown in fig. 1 is referred to as the Z direction, and a cross section of the waveguide element 10 parallel to the XZ plane is schematically shown. In the waveguide element 10, a pair of mirrors 30 and 40 are arranged so as to sandwich the optical waveguide layer 20. The light 22 introduced from one end of the optical waveguide layer 20 in the X direction propagates in the optical waveguide layer 20 while being repeatedly reflected by the 1 st mirror 30 provided on the upper surface (upper surface in fig. 2) of the optical waveguide layer 20 and the 2 nd mirror 40 provided on the lower surface (lower surface in fig. 2). The 1 st mirror 30 has a higher light transmittance than the 2 nd mirror 40. Therefore, a part of the light can be output mainly from the 1 st mirror 30.

In a typical waveguide such as an optical fiber, light propagates along the waveguide while repeating total reflection. In contrast, in the waveguide element 10 of the present invention, light propagates while being repeatedly reflected by the mirrors 30 and 40 disposed on the upper and lower sides of the optical waveguide layer 20. Therefore, there is no restriction on the propagation angle of light. Here, the propagation angle of light is an incident angle directed to the interface of the mirror 30 or the mirror 40 and the optical waveguide layer 20. Light incident at angles closer to normal to either mirror 30 or mirror 40 can also propagate. That is, light incident on the interface at an angle smaller than the critical angle for total reflection can also propagate. Therefore, the group velocity of light in the propagation direction of light is greatly reduced compared with the light velocity in the free space. Thus, the waveguide element 10 has the following properties: the propagation conditions of light vary greatly with respect to the wavelength of light, the thickness of the optical waveguide layer 20, and the change in refractive index of the optical waveguide layer 20. The waveguide element 10 is also referred to as a "reflective waveguide" or "slow optical waveguide".

The emission angle θ of the light emitted from the waveguide 10 into the air is expressed by the following expression (1).

[ number 1]

As can be seen from the formula (1), by changing the wavelength lambda of light in the air and the refractive index n of the optical waveguide layer 20 _w And the thickness d of the optical waveguide layer 20, the light emission direction can be changed.

For example, at n _w When =2, d=387 nm, λ=1550nm, and m=1, the emission angle is 0 °. If the refractive index is changed from this state to n _w =2.2, the emission angle varies to about 66 °. On the other hand, if the thickness is changed to d=420 nm without changing the refractive index, the emission angle is changed to about 51 °. If the wavelength is changed to λ=1500 nm without changing the refractive index and the thickness, the emission angle is changed to about 30 °. By thus adjusting the wavelength lambda of the light and the refractive index n of the optical waveguide layer 20 _w Light and method for producing the sameThe thickness d of the waveguide layer 20 can be changed to greatly change the light emission direction.

Therefore, in the optical scanning device 100 of the present invention, the wavelength λ of the light input to the optical waveguide layer 20 and the refractive index n of the optical waveguide layer 20 are controlled _w And the thickness d of the optical waveguide layer 20 to control the light emission direction. The wavelength λ of light may be kept constant without being changed during operation. In this case, scanning of light can be achieved with a simpler structure. The wavelength λ is not particularly limited. For example, the wavelength λ may be included in a wavelength range of 400nm to 1100nm (from visible light to near infrared light) that can obtain high detection sensitivity by a general photodetector or image sensor that detects light by absorbing light with silicon (Si). In another example, the wavelength λ may be included in a wavelength region of near infrared light having a relatively small transmission loss of 1260nm to 1625nm in an optical fiber or Si waveguide. These wavelength ranges are examples. The wavelength range of the light to be used is not limited to the wavelength range of visible light or infrared light, and may be, for example, the wavelength range of ultraviolet light.

In order to change the direction of the emitted light, the optical scanning device 100 may include a 1 st adjustment element that changes at least one of the refractive index, thickness, and wavelength of the optical waveguide layer 20 in each waveguide element 10.

As described above, if the waveguide element 10 is used, the refractive index n of the optical waveguide layer 20 is obtained by _w At least one of the thickness d and the wavelength λ is changed, so that the light emission direction can be greatly changed. This allows the angle of light emitted from the mirror 30 to be varied in the direction along the waveguide 10. Such a one-dimensional scan can be achieved by using at least one waveguide element 10.

The optical waveguide layer 20 may also contain a liquid crystal material or an electro-optical material in order to adjust the refractive index of at least a portion of the optical waveguide layer 20. The optical waveguide layer 20 can be sandwiched between a pair of electrodes. By applying a voltage to the pair of electrodes, the refractive index of the optical waveguide layer 20 can be changed.

For adjusting the thickness of the optical waveguide layer 20, at least one actuator may be connected to at least one of the 1 st mirror 30 and the 2 nd mirror 40, for example. The thickness of the optical waveguide layer 20 can be varied by varying the distance between the 1 st mirror 30 and the 2 nd mirror 40 by at least one actuator. If the optical waveguide layer 20 is formed of a liquid, the thickness of the optical waveguide layer 20 can be easily changed.

< principle of action of two-dimensional scanning >

In a waveguide array in which a plurality of waveguide elements 10 are arranged in one direction, the light emission direction changes by interference of light emitted from each waveguide element 10. By adjusting the phase of the light supplied to each waveguide element 10, the light emission direction can be changed. The principle thereof will be described below.

Fig. 3A is a view showing a cross section of a waveguide array that emits light in a direction perpendicular to an emission surface of the waveguide array. In fig. 3A, the phase shift amount of light propagating through each waveguide element 10 is also shown. Here, the phase shift amount is a value based on the phase of light propagating through the waveguide element 10 at the left end. The waveguide array of the present invention includes a plurality of waveguide elements 10 arranged at equal intervals. In fig. 3A, the circular arcs of the broken lines represent wave surfaces of light emitted from the respective waveguide elements 10. The straight line represents a wavefront formed by interference of light. The arrow indicates the direction of light (i.e., the direction of the wavenumber vector) exiting the waveguide array. In the example shown in fig. 3A, the phases of light propagating in the optical waveguide layers 20 in the respective waveguide elements 10 are all the same. In this case, the light is emitted in a direction (Z direction) perpendicular to both the arrangement direction (Y direction) of the waveguide elements 10 and the direction (X direction) in which the optical waveguide layer 20 extends.

Fig. 3B is a view showing a cross section of the waveguide array which emits light in a direction different from the direction perpendicular to the emission surface of the waveguide array. In the example shown in fig. 3B, the phases of light propagating in the optical waveguide layers 20 in the plurality of waveguide elements 10 each differ by a certain amount (ΔΦ) in the arrangement direction. In this case, the light is emitted in a direction different from the Z direction. By changing this ΔΦ, the component in the Y direction of the wave number vector of light can be changed. If the center-to-center distance between two adjacent waveguide elements 10 is p, the light emission angle α ₀ Represented by the following formula (2).

[ number 2]

In the example shown in fig. 2, the light emission direction is parallel to the XZ plane. I.e. alpha ₀ =0°. In the example shown in fig. 3A and 3B, the direction of light emitted from the optical scanning apparatus 100 is parallel to the YZ plane. I.e., θ=0°. However, the direction of light emitted from the light scanning apparatus 100 is generally not parallel to either the XZ plane or the YZ plane. That is, θ+.0° and α ₀ ≠0°。

Fig. 4 is a perspective view schematically showing an example of a waveguide array in a three-dimensional space. The thick arrows shown in fig. 4 indicate the directions of light emitted from the optical scanning apparatus 100. θ is the angle formed between the light emission direction and the YZ plane. θ satisfies formula (1). Alpha ₀ Is the angle formed by the light emission direction and the XZ plane. Alpha ₀ Satisfying the formula (2).

< phase control of light introduced into waveguide array >

In order to control the phase of the light emitted from each waveguide element 10, a phase shifter for changing the phase of the light may be provided at a front stage where the light is introduced into the waveguide element 10, for example. The optical scanning device 100 of the present invention includes a plurality of phase shifters connected to each of the plurality of waveguide elements 10, and a 2 nd adjustment element for adjusting the phase of light propagating through each of the phase shifters. Each phase shifter includes a waveguide connected to the optical waveguide layer 20 in a corresponding one of the plurality of waveguide elements 10 directly or via other waveguides. The 2 nd adjustment element changes the direction of light emitted from the plurality of waveguide elements 10 (i.e., the 3 rd direction D3) by changing the difference in the phases of light propagating from the plurality of phase shifters to the plurality of waveguide elements 10. In the following description, a plurality of arrayed phase shifters are sometimes referred to as a "phase shifter array" as in the waveguide array.

Fig. 5 is a schematic view of the waveguide array 10A and the phase shifter array 80A as viewed from the normal direction (Z direction) of the light emitting surface. In the example shown in fig. 5, all of the phase shifters 80 have the same propagation characteristics, and all of the waveguide elements 10 have the same propagation characteristics. The respective phase shifters 80 and the respective waveguide elements 10 may have the same length or may have different lengths. In the case where the lengths of the respective phase shifters 80 are equal, for example, the respective phase shift amounts may be adjusted by the driving voltages. Further, by changing the lengths of the phase shifters 80 in equal steps, equal-step phase shifting can be applied to the same driving voltage. The optical scanning device 100 further includes a beam splitter 90 for branching light and supplying the branched light to the plurality of phase shifters 80, a 1 st driving circuit 110 for driving each waveguide element 10, and a 2 nd driving circuit 210 for driving each phase shifter 80. The straight arrows shown in fig. 5 represent the input of light. By controlling the 1 st driving circuit 110 and the 2 nd driving circuit 210 provided separately, respectively, independently, two-dimensional scanning can be achieved. In this example, the 1 st driving circuit 110 functions as one element of the 1 st adjustment element, and the 2 nd driving circuit 210 functions as one element of the 2 nd adjustment element.

The 1 st driving circuit 110 changes the angle of the light emitted from the optical waveguide layer 20 by changing at least one of the refractive index and the thickness of the optical waveguide layer 20 in each waveguide element 10. The 2 nd drive circuit 210 changes the phase of the light propagating through the optical waveguide 20a by changing the refractive index of the optical waveguide 20a in each phase shifter 80. The beam splitter 90 may be configured by a waveguide that propagates light by total reflection, or may be configured by a reflective waveguide similar to the waveguide element 10.

In addition, after the phase of each light branched by the beam splitter 90 is controlled, each light may be introduced into the phase shifter 80. For example, a simple phase control structure realized by adjusting the length of the waveguide to the phase shifter 80 can be used for the phase control. Alternatively, a phase shifter that can be controlled by an electric signal and has the same function as the phase shifter 80 may be used. By such a method, for example, the phase may be adjusted before the light is introduced into the phase shifters 80, so that the light having the same phase may be supplied to all the phase shifters 80. By such adjustment, the control of each phase shifter 80 by the 2 nd drive circuit 210 can be simplified.

An optical device having the same configuration as the optical scanning device 100 described above can also be used as the light receiving device. Details of the operation principle, operation method, and the like of the optical device are disclosed in U.S. patent application publication No. 2018/0224709. The entire disclosure of this document is incorporated in the present specification.

< connection of Total reflection waveguide and Slow optical waveguide >

Next, an example will be described in which the total reflection waveguide and the slow optical waveguide are connected to each other, and light is inputted from the total reflection waveguide to the slow optical waveguide.

Fig. 6 is a cross-sectional view schematically showing an example of an optical device to which the total reflection waveguide 1 and the slow optical waveguide 10 are connected. In the present specification, the total reflection waveguide 1 is sometimes referred to as "1 st waveguide 1", and the slow optical waveguide 10 is sometimes referred to as "2 nd waveguide 10". The optical device shown in fig. 6 will be described without considering the shape of the end 30e of the 1 st mirror 30.

In the total reflection waveguide 1, at least the tip portion has a configuration extending in the X direction. The slow optical waveguide 10 is connected to the total reflection waveguide 1. The optical waveguide layer 20 in the slow optical waveguide 10 internally includes a portion including the front end portion of the total reflection waveguide 1. The refractive index of the optical waveguide layer 20 is lower than that of the total reflection waveguide 1. In the connection region 111 where the total reflection waveguide 1 and the slow optical waveguide 10 overlap when viewed from the Z direction, the total reflection waveguide 1 includes a grating 15 whose refractive index changes with a period p along the X direction. The connection region 111 can be said to be a region where the 1 st mirror 30, the 2 nd mirror 40, and the total reflection waveguide 1 overlap when viewed from the Z direction. The grating 15 shown in fig. 6 has 4 concave portions arranged in the X direction. In practice, more recesses may be provided in the grating 15. Instead of the concave portion, a convex portion may be provided. The number of concave portions or convex portions of the grating 15 aligned in the X direction is preferably, for example, 4 or more. The number of concave portions or convex portions may be 4 or more and 64 or less. In one example, the number of concave portions or convex portions may be 8 or more and 32 or less. In one example, the number of concave portions or convex portions may be 8 or more and 16 or less. The number of concave portions or convex portions can be adjusted according to the diffraction efficiency of each concave portion or convex portion. The diffraction efficiency of each concave or convex portion depends on the dimensional conditions such as the depth and width. Therefore, the number of the concave portions and the convex portions is adjusted according to the size of each concave portion and each convex portion, so that good characteristics can be obtained as a whole of the grating 15.

The total reflection waveguide 1 has a 1 st surface 1s facing the reflection surface of the 1 st mirror 30 in the connection region 111 ₁ And a 2 nd surface 1s opposed to the reflection surface of the 2 nd mirror 40 ₂ . In the example shown in FIG. 6, the grating 15 is provided on the 1 st surface 1s of the total reflection waveguide 1 ₁ . The grating 15 may also be disposed on the 2 nd surface 1s ₂ . The grating 15 may be disposed on the 1 st surface 1s of the total reflection waveguide 1 ₁ 2 nd surface 1s ₂ At least one of (2).

The grating 15 is not limited to the interface between the total reflection waveguide 1 and the slow optical waveguide 10, and may be provided at another position. In addition, a plurality of gratings may be provided. In the connection region 111 where the total reflection waveguide 1 and the slow optical waveguide 10 overlap when viewed from the direction perpendicular to the reflection surface of the 1 st mirror 30, at least a part of the total reflection waveguide 1 and the slow optical waveguide 10 may include at least 1 grating. The refractive index of each grating changes periodically along the X direction in which the total reflection waveguide 1 and the slow optical waveguide 10 extend.

In the total reflection waveguide 1, the portion located outside the optical waveguide layer 20 may be supported by another dielectric layer or may be sandwiched between 2 dielectric layers.

The length of the connection region 111 may be, for example, about 3 μm to 50 μm. Inside the connection region 111 of such a size, the grating 15 of about 8 cycles to 32 cycles can be formed. The length of the non-connection region 112 may be, for example, about 100 μm to 5 mm. The length of the connection region 111 may be, for example, about one hundredth to one tenth of the length of the non-connection region 112. However, the length is not limited to this length, and the dimensions of the respective members may be determined according to the characteristics required.

In the connection region 111, the 1 st mirror 30 may not have a higher transmittance than the 2 nd mirror 40. In the non-connection region 112 other than the connection region 111 in the slow optical waveguide 10, the 1 st mirror 30 may not have a higher transmittance than the 2 nd mirror 40 in a region near the connection region 111. The connection region 111 is provided to improve light coupling efficiency. Therefore, the slow optical waveguide 10 does not necessarily need to emit light in the vicinity of the connection region 111.

Let the propagation constant of the waveguide mode of the total reflection waveguide 1 be beta ₁ ＝2πn _e1 Let the propagation constant of the waveguide mode of the slow optical waveguide 10 be beta ₂ ＝2πn _e2 λ. Lambda is the wavelength of light in air. n is n _e1 N is as follows _e2 The effective refractive index (also referred to as equivalent refractive index) in the total reflection waveguide 1 and the slow optical waveguide 10, respectively. Light propagating within the total reflection waveguide 1 is not coupled with the outside air. The effective refractive index of such a waveguide mode is n _e1 >1. On the other hand, a part of the light propagating through the optical waveguide layer 20 of the slow optical waveguide 10 is emitted to the outside air. The effective refractive index of such a waveguide mode is 0<n _e2 <1. Thus, beta ₁ And beta ₂ Is greatly different. Therefore, the coupling efficiency of waveguide light from the total reflection waveguide 1 to the slow optical waveguide 10 is generally low.

In the connection region 111, when the total reflection waveguide 1 includes the grating 15, diffraction by the grating 15 occurs. In this case, the propagation constant β of the waveguide mode of the total reflection waveguide 1 ₁ Shifting the reciprocal lattice by an integer multiple of 2 pi/p. For example in beta by-1 st diffraction ₁ Shifted to beta ₁ In the case of- (2π/p), β can be made by appropriately setting p ₁ －(2π/p)＝β ₂ This is true. In this case, since 2 propagation constants of the connection region 111 are uniform, waveguide light is coupled from the total reflection waveguide 1 to the slow optical waveguide 10 with high efficiency. According to beta ₁ －(2π/p)＝β ₂ The period p is represented by the following formula (3).

[ number 3]

Due to 0<n _e2 <1, the period p satisfies the following expression (4).

[ number 4]

In the slow optical waveguide 10, the same waveguide mode is present in the connection region 111 and the non-connection region 112 other than the connection region, so that waveguide light is coupled with high efficiency.

In the above example, the grating is provided in the entire connection region 111 where the 1 st waveguide 1 and the 2 nd waveguide 10 overlap. However, the structure of the optical device of the present invention is not limited to such a structure. The grating may be provided only in a part of the connection region 111, for example, in a portion of the connection region 111 near the front end of the 1 st waveguide 1. In other words, the grating may not be provided in a portion of the connection region 111 distant from the front end of the 1 st waveguide 1. In one embodiment of the present invention, 1 or more gratings are provided at positions separated in the 1 st direction by a distance longer than at least one of the thickness of the 1 st mirror 30 and the thickness of the 2 nd mirror 40 from the interface between the medium (for example, air) and the optical waveguide layer 20, which interfaces with both the optical waveguide layer 20 and the 1 st waveguide 1. The study by the inventors of the present invention revealed that by such a configuration, good light emission characteristics are easily achieved even in the case where the thickness of the optical waveguide layer 20 is not uniform.

In the above example, it is assumed that the thickness of the optical waveguide layer 20 is constant along the X direction. However, in practice, the thickness of the optical waveguide layer 20 may vary along the X direction for various reasons. The influence of the thickness change of the optical waveguide layer 20 along the X direction will be described in detail below. In the following description, the number of gratings is 1, but the number of gratings may be 2 or more.

Fig. 7 is a diagram showing an example of a calculation result of a relationship between a change rate of the thickness of the optical waveguide layer 20 and a diffusion angle of the light emitted from the 1 st mirror 30. The range of the rate of change in the thickness of the optical waveguide layer 20 in the example of fig. 7 is 0nm/mm to 100nm/mm. Here, the "rate of change of thickness" refers to the amount of change in thickness with respect to a displacement of 1mm along the length direction of the optical waveguide layer 20, i.e., the 1 st direction. 0nm/mm means that the thickness of the optical waveguide layer 20 does not substantially change along the X direction. 100nm/mm means that the thickness of the optical waveguide layer 20 varies by 100nm with respect to a displacement of 1mm along the length direction of the optical waveguide layer 20.

In this calculation, the thickness of the optical waveguide layer 20 was set to 2.15 μm, the refractive index was set to 1.68, and a waveguide in which the thickness of the optical waveguide layer 20 was changed along the X direction was assumed. The complex amplitude of the light emitted from the emission surface of the 1 st mirror 30 is obtained, and the two-dimensional discrete fourier transform is applied thereto to calculate the angular spectrum of the light emitted from a distance. In the following description, it is assumed that the diffusion angle of the emitted light is the full width at half maximum of the emitted light in the angular spectrum.

As shown in fig. 7, when the rate of change in the thickness of the optical waveguide layer 20 is about 10nm/mm, the diffusion angle of the emitted light is substantially the same as when the thickness of the optical waveguide layer 20 is constant. However, when the rate of change in the thickness of the optical waveguide layer 20 is 20nm/mm or more, the diffusion angle of the emitted light increases substantially monotonously with respect to the inclination of the optical waveguide layer 20. Such diffusion of the emitted light is due to the disturbance of the phase distribution of the light emitted from the 1 st mirror 30 due to the uneven thickness of the optical waveguide layer 20. If the diffusion angle of the emitted light is large, the linear transmissibility of the emitted light is lost. In particular, in the connection region 111 where the total reflection waveguide 1 and the slow optical waveguide 10 are connected, the intensity of the light emitted from the 1 st mirror 30 is higher than that of the light further advancing from the connection region 111. Therefore, if the thickness of the optical waveguide layer 20 in the connection region 111 is not constant, there is a possibility that the relatively strong light emitted from the 1 st mirror 30 in the connection region 111 is excessively diffused.

As a cause of the thickness variation of the optical waveguide layer 20, a shape variation of the end portion of the 1 st mirror 30 by processing can be considered. As shown in fig. 6, the end 30e of the 1 st mirror 30 may be inclined by etching, for example. Further, as another cause of the thickness variation of the optical waveguide layer 20, warpage of the 1 st mirror 30 and/or the 2 nd mirror 40 may be considered.

An example of an optical device that suppresses the influence of the change in the thickness of the optical waveguide layer 20 will be described below.

Fig. 8A is a diagram schematically showing an optical apparatus according to an exemplary embodiment of the present invention. The surrounding medium of the light device is for example air. Medium and optical waveguide connected to both of optical waveguide layer 20 and total reflection waveguide 1The interface 20i of the layer 20 encloses the total reflection waveguide 1. In the present embodiment, the ends of the 1 st mirror 30 and the 2 nd mirror 40 in the X direction coincide. Therefore, the end face 20i of the connection region 111 of the present embodiment is a face passing through the end portions of the 1 st mirror 30 and the 2 nd mirror 40 and parallel to the Y direction and the Z direction. The end face 20i is an end of the connection region 111 of the present embodiment. In the present embodiment, the interface 20i between the medium and the optical waveguide layer 20 corresponds to the end face 20i of the connection region 111. As shown in fig. 8A, the grating 15 is located further inside the optical waveguide layer 20 from the end 30e of the 1 st mirror 30 than in the example shown in fig. 6. When the length of the inclined portion of the end portion 30e of the 1 st mirror 30 when projected in the X direction exceeds the thickness of the 1 st mirror 30, such 1 st mirror 30 is not used in the optical device from the viewpoint of reliability. Therefore, in the 1 st mirror 30 actually used for the optical device, the length of the inclined portion of the end portion 30e when projected in the X direction is equal to or less than the thickness of the 1 st mirror 30. The thickness of the 1 st mirror 30 may be 3 μm, for example. The same applies to the case where the 2 nd mirror 40 has an end surface like the 1 st mirror 30 in the vicinity of the end surface 20 i. Therefore, in order to suppress the influence of the change in the thickness of the optical waveguide layer 20, the grating 15 may be disposed at a distance longer than at least one of the thickness of the 1 st mirror 30 and the thickness of the 2 nd mirror 40 in the X direction from the end surface 20 i. In other words, the distance L in the X direction from the end face 20i to the grating 15 ₀ Longer than at least one of the thickness of the 1 st mirror 30 and the thickness of the 2 nd mirror 40. Here, the distance L from the end face 20i to the grating 15 ₀ Refers to the distance from the end face 20i to the end face 20i, which is closer to the end face 20i, among the 2 end portions of the grating 15.

Fig. 8B is a schematic diagram of the connection of the total reflection waveguide 1 and the slow optical waveguide 10 shown in fig. 8A as viewed from the Z direction. In the example shown in fig. 8B, the total reflection waveguide 1 includes a portion whose width monotonically increases as approaching the slow optical waveguide 10, outside the optical waveguide layer 20 in the total reflection waveguide 1. That is, a part of the total reflection waveguide 1 has a taper configuration 1t. Width w of total reflection waveguide 1 at a portion distant from optical waveguide layer 20 _w Narrower than the width wc of the total reflection waveguide 1 in the connection region 111 as a coupling portion. Width w _w May be width w _c For example, 1 per 100To about 1 per 2. In the total reflection waveguide 1, a taper configuration 1t exists between a waveguide portion 1w having a narrower width and a waveguide portion 1c having a wider width. With such a configuration, reflection of light propagating through the waveguide portion 1w having a narrow width when the light enters the waveguide portion 1c having a wide width can be suppressed.

In addition, the warpage of the 1 st mirror 30 and/or the 2 nd mirror 40 is smallest near the center in the X direction of the 1 st mirror 30 and/or the 2 nd mirror 40. Therefore, the grating 15 may be located near the center in the X direction of the 1 st mirror 30 and/or the 2 nd mirror 40 in the optical waveguide layer 20. On the other hand, the distance L from the end face 20i to the grating 15 ₀ In the shorter time, the probability of occurrence of defects and/or particles at the portion of the total reflection waveguide 1 located inside the optical waveguide layer 20 becomes smaller. Thus, the distance L from the end face 20i to the grating 15 ₀ Length L of grating 15 _g Is the sum L of ₀ +L _g It may be shorter than one of the half length of the 1 st mirror 30 and the half length of the 2 nd mirror 40. L (L) ₀ +L _g Corresponding to the length of the connection region 111 shown in fig. 8A. The length of the entire 1 st mirror 30 and 2 nd mirror 40 shown in fig. 8A is not particularly limited, and may be 300 μm or more and 10mm or less, for example. In one example, the length may be 1mm or more and 5mm or less, for example, about 2mm.

The connection region 111 may be divided into a 1 st connection region 111a containing no grating and a 2 nd connection region 111b containing the grating 15. The 1 st connection region 111a has a length L ₀ The length of the 2 nd connection region 111b is L _g . Length L of 1 st connection region 111a ₀ For example, the thickness may be 3 μm or more and 1mm or less. The length L ₀ It may be 10 μm or more and 1mm or less. In other examples, the length L ₀ It may be set to 150 μm or more and 1mm or less.

Next, a distance L from the end face 20i to the grating 15 will be described ₀ Examples of longer optical devices.

FIG. 9 schematically shows the distance L from the end face 20i to the grating 15 ₀ A diagram of an example of a longer optical device. Distance L from end face 20i to grating 15 ₀ For example, the optical waveguide may be set to be longer in the X direction than in the slow optical waveguide 10The attenuation distance required for the intensity of the propagating light to attenuate to 1/e times is long. e is the base of the natural logarithm. The decay distance may be, for example, about 150 μm to about 200 μm or more. The attenuation distance may be several tenths or more of the length of the region where the 1 st mirror 30 and the 2 nd mirror 40 overlap when viewed from the Z direction. When the expression (3) is not satisfied, the light propagating in the total-reflection waveguide 1 does not propagate to the non-connection region 112, but is reflected by the end face 1e of the total-reflection waveguide 1 in the optical waveguide layer 20. A part of the reflected light leaks into the optical waveguide layer 20 in the connection region 111, and propagates in the-X direction. This allows light propagating in the-X direction in the optical waveguide layer 20 to be emitted rearward from the 1 st mirror 30 in the connection region 111. Further, when the optical waveguide layer 20 includes a liquid crystal material or an electro-optical material, the refractive index of the optical waveguide layer 20 is adjusted so as to satisfy the expression (3), whereby the light emission direction can be switched from the rear to the front and vice versa. The term "forward" means that the light emitted from the slow optical waveguide 10 has a component in the +x direction from the total reflection waveguide 1 toward the slow optical waveguide 10. "backward" means that the light emitted from the slow optical waveguide 10 has a component in the-X direction from the slow optical waveguide 10 toward the total reflection waveguide 1. Next, a modification of the connection between the total reflection waveguide 1 and the slow optical waveguide 10 via the grating 15 will be described. The following modification described with reference to fig. 10A to 10C and fig. 11A and 11B is common to the example shown in fig. 8A in that the grating 15 is located further inside than the optical waveguide layer 20.

Fig. 10A to 10C are cross-sectional views schematically showing a modification of the optical device shown in fig. 8A. In the example shown in fig. 10A to 10C, the total reflection waveguide 1 is supported by the dielectric layer 51, and the dielectric layer 51 is supported by the 2 nd mirror 40. The 2 nd mirror 40 is shared by the total reflection waveguide 1 and the slow optical waveguide 10. The dielectric layer 51 is made of, for example, siO ₂ And (5) forming. Refractive index n of dielectric layer 51 _sub Refractive index n of the total reflection waveguide 1 _w1 Is small. Thus, light propagating in the total reflection waveguide 1 does not leak to the dielectric layer 51. The dielectric layer 51 may not be supported by the 2 nd mirror 40. In regions other than the connection region 111 and the non-connection region 112, the 2 nd mirror 40 may be replaced with a dielectric layer51 of the same material. The end surface of the connection region 111 of the present modification is a surface passing through the end of the 1 st mirror 30 and parallel to the Y direction and the Z direction. The end face is an end of the connection region 111 of the present embodiment.

In the example shown in FIG. 10A, the total reflection waveguide 1 is provided at the 1 st surface 1s ₁ Is provided with a grating 15. In the example shown in FIG. 10B, the total reflection waveguide 1 is at the 2 nd surface 1s ₂ Is provided with a grating 15. In the example shown in FIG. 10C, the total reflection waveguide 1 is at the 1 st surface 1s ₁ 2 nd surface 1s ₂ Both of them have a grating 15.

Thus, the total reflection waveguide 1 can be formed on the 1 st surface 1s ₁ 2 nd surface 1s ₂ At least one of which is provided with a grating 15.

Fig. 11A and 11B are cross-sectional views schematically showing other modifications of the optical device shown in fig. 8A. In the example shown in fig. 11A and 11B, the total reflection waveguide 1 is supported by the dielectric layer 51, and the dielectric layer 51 is supported by the 2 nd mirror 40, as in the example shown in fig. 10A to 10C.

In the example of fig. 11A and 11B, the grating 15 is provided not on the total reflection waveguide 1 but on the reflection surface of the 1 st mirror 30 and/or the 2 nd mirror 40. In the example shown in fig. 11A, the slow optical waveguide 10 includes a grating 15 on the reflection surface of the 1 st mirror 30. In the example shown in fig. 11B, the slow optical waveguide 10 is provided with a grating 15 on the reflective surface of the 2 nd mirror 40.

In the example shown in fig. 11A and 11B, the distance in the Z direction between the total reflection waveguide 1 and the 1 st mirror 30 and/or the 2 nd mirror 40 is relatively short. Thereby, the evanescent light in the total reflection waveguide 1 is diffracted by the grating 15. As a result, as in the above example, the coupling efficiency of waveguide light from the total reflection waveguide 1 to the slow optical waveguide 10 can be improved. In this way, the slow optical waveguide 10 may include the grating 15 on at least one of the reflection surface of the 1 st mirror 30 and the reflection surface of the 2 nd mirror 40.

As shown in fig. 8A, 10A to 10C and 11A and 11B, at least one of the total reflection waveguide 1 and the slow optical waveguide 10 has a grating 15 at a part of a portion where the total reflection waveguide 1 and the slow optical waveguide 10 overlap when viewed from the Z direction.

As shown in fig. 10A to 10C and fig. 11A and 11B, the total reflection waveguide 1 shown in fig. 9 may be supported by the dielectric layer 51 on the 2 nd mirror 40.

Next, functions that the above-described components of the optical device may have will be described.

At least a part of the optical waveguide layer 20 may have a structure capable of adjusting the refractive index and/or thickness. By adjusting the refractive index and/or thickness, the component in the X direction among the directions of the light emitted from the 1 st mirror 30 changes.

In the optical waveguide layer 20, the refractive index in the connection region 111 and the refractive index in the non-connection region 112 may also be adjusted at the same time. However, if the refractive index in the connection region 111 is adjusted, the condition of formula (3) may vary. As a result, the coupling efficiency of waveguide light from the total reflection waveguide 1 to the slow optical waveguide 10 may be lowered. Therefore, the refractive index in the connection region 111 may be maintained constant so that only the refractive index in the non-connection region 112 can be adjusted. Even if the refractive indices in the connection region 111 and the non-connection region 112 are different, the influence of reflection of waveguide light occurring at the interface of the connection region 111 and the non-connection region 112 is small.

In this case, the pair of electrodes (also referred to as "the 1 st pair of electrodes") sandwich a portion of the optical waveguide layer 20 different from a portion overlapping the total reflection waveguide 1 when viewed from a direction perpendicular to the reflection surface of the 1 st mirror 30. By applying a voltage to the pair of electrodes by a control circuit, not shown, the refractive index of at least a part of the non-connection region 112 can be adjusted.

However, in practice, the condition of the formula (3) may not be completely satisfied due to manufacturing errors, as long as the condition of the formula (3) is satisfied as designed. For compensation in such a case, a function of adjusting the refractive index of the connection region 111 may be given to the optical device in addition to the adjustment of the refractive index in the non-connection region 112.

In this case, a 2 nd pair of electrodes may be provided in addition to the 1 st pair of electrodes. At least a part of the portion of the optical waveguide layer 20 overlapping the total reflection waveguide when viewed from the Z direction is sandwiched between the 2 nd pair of electrodes. The control circuit can independently adjust the refractive index of the portion of the optical waveguide layer located between the 1 st pair of electrodes and the refractive index of the portion of the optical waveguide layer located between the 2 nd pair of electrodes by independently applying voltages to the 1 st pair of electrodes and the 2 nd pair of electrodes.

For adjusting the thickness of the optical waveguide layer 20, at least 1 actuator may be connected to at least one of the 1 st mirror 30 and the 2 nd mirror 40, for example. The control circuit can change the thickness of the optical waveguide layer 20 by changing the distance between the 1 st mirror 30 and the 2 nd mirror 40 by controlling at least 1 actuator. If the optical waveguide layer 20 is formed of a liquid, the thickness of the optical waveguide layer 20 can be easily changed.

The at least 1 actuator may be connected to at least one of the 1 st mirror 30 and the 2 nd mirror 40 in the non-connection region 112. By the actuator, the thickness of the optical waveguide layer 20 in the non-connection region 112 can be changed. At this time, the condition of the formula (3) does not change.

The at least 1 actuator may be 2 actuators. One actuator may be connected to at least one of the 1 st mirror 30 and the 2 nd mirror 40 in the connection region 111. The other actuator may be connected to at least one of the 1 st mirror 30 and the 2 nd mirror 40 in the non-connection region 112. The thickness of the optical waveguide layer 20 in the connection region 111 and the thickness of the optical waveguide layer 20 in the non-connection region 112 can be individually varied by 2 actuators. This makes it possible to compensate for the condition that does not satisfy the expression (3) as designed.

By configuring the optical device including the plurality of groups of the total reflection waveguide 1 and the slow optical waveguide 10, two-dimensional optical scanning can be performed. Such an optical scanning device is provided with a plurality of waveguide units arranged in the Y direction. Each waveguide unit includes the total reflection waveguide 1 and the slow optical waveguide 10. In the optical scanning device, a plurality of phase shifters are connected to a plurality of waveguide units, respectively. The plurality of phase shifters each include a waveguide connected directly or via other waveguides to the total reflection waveguide 1 in the corresponding 1 of the plurality of waveguide units. By varying the phase difference of the light passing through the plurality of phase shifters, the component in the Y direction among the directions of the light emitted from the optical scanning device can be varied. The light receiving device can be constituted by the same configuration.

< application example >

Fig. 12 is a diagram showing a configuration example of an optical scanning device 100 in which elements such as a beam splitter 90, a waveguide array 10A, a phase shifter array 80A, and a light source 130 are integrated on a circuit board (e.g., a chip). The light source 130 may be a light emitting element such as a semiconductor laser, for example. The light source 130 in this example emits light of a single wavelength in free space having a wavelength λ. The beam splitter 90 branches light from the light source 130 and guides the light to the waveguides of the plurality of phase shifters. In the example shown in fig. 12, an electrode 62A and a plurality of electrodes 62B are provided on a chip. For the waveguide array 10A, a control signal is supplied from the electrode 62A. For a plurality of phase shifters 80 in the phase shifter array 80A, control signals are transmitted from the plurality of electrodes 62B, respectively. The electrode 62A and the plurality of electrodes 62B can be connected to a control circuit, not shown, that generates the control signal. The control circuit may be provided on the chip shown in fig. 12 or on another chip of the optical scanning apparatus 100.

As shown in fig. 12, by integrating all the components on a chip, a large-scale optical scanning can be achieved with a small-sized device. For example, all the components shown in fig. 12 can be integrated on a chip of about 2mm×1 mm.

Fig. 13 is a schematic diagram showing a situation in which a two-dimensional scanning is performed by irradiating a light beam such as a laser beam from the optical scanning apparatus 100 to a distant place. The two-dimensional scanning is performed by moving the beam spot 310 in the horizontal and vertical directions. For example, a two-dimensional ranging image can be obtained by combining a known TOF (Time Of Flight) method. The TOF method is a method of calculating the time of flight of light and finding the distance by irradiating laser light and observing reflected light from an object.

Fig. 14 is a block diagram showing a configuration example of a LiDAR system 300 as an example of a light detection system capable of generating such a range image. LiDAR system 300 includes light scanning device 100, light detector 400, signal processing circuit 600, and control circuit 500. The photodetector 400 detects light emitted from the light scanning device 100 and reflected from the object. The photodetector 400 may be, for example, an image sensor having sensitivity to the wavelength λ of light emitted from the optical scanning device 100, or a photodetector including a light receiving element such as a photodiode. The photodetector 400 outputs an electrical signal corresponding to the amount of light received. The signal processing circuit 600 calculates a distance to the object based on the electric signal output from the photodetector 400, and generates distance distribution data. The distance distribution data is data representing a two-dimensional distribution of distances (i.e., ranging images). The control circuit 500 is a processor that controls the optical scanning device 100, the optical detector 400, and the signal processing circuit 600. The control circuit 500 controls the timing of irradiation of the light beam from the optical scanning device 100 and the timing of exposure and signal readout of the photodetector 400, and instructs the signal processing circuit 600 to generate a ranging image.

In the two-dimensional scanning, the frame rate at which the range-finding image is obtained may be selected from, for example, 60fps, 50fps, 30fps, 25fps, 24fps, and the like, which are commonly used in moving images. Further, if the application to the in-vehicle system is considered, the higher the frame rate is, the higher the frequency of acquiring the range image is, and the more accurate the obstacle can be detected. For example, at 60km/h of travel, at a frame rate of 60fps, images can be taken every time the vehicle moves by about 28 cm. At a frame rate of 120fps, images can be taken every time the vehicle moves about 14 cm. At a frame rate of 180fps, images can be taken every time the vehicle moves about 9.3 cm.

The time required to acquire a range finding image depends on the speed of the beam scan. For example, in order to obtain an image with a resolution of 100×100 at 60fps, it is necessary to perform beam scanning at 1.67 μs or less per 1 point. In this case, the control circuit 500 controls the emission of the light beam by the optical scanning device 100 and the accumulation and readout of the signal by the photodetector 400 at an operation speed of 600 kHz.

< application example of light receiving device >

The optical scanning device of the present invention can also be used as a light receiving device in substantially the same configuration. The light receiving device includes the same waveguide array 10A as the light scanning device, and a 1 st adjustment element that adjusts the direction of receivable light. Each 1 st mirror 30 of the waveguide array 10A transmits light incident from the 3 rd direction to the opposite side of the 1 st reflection surface. Each optical waveguide layer 20 of the waveguide array 10A propagates the light transmitted through the 1 st mirror 30 in the 2 nd direction. The 1 st adjustment element can change the direction of the receivable light by changing at least one of the refractive index and thickness of the optical waveguide layer 20 and the wavelength of the light in each waveguide element 10. Further, in the case where the light receiving device includes the same plurality of phase shifters 80, or 80a and 80b as the light scanning device, and the 2 nd adjustment element for changing the difference in phase of the light outputted from the plurality of waveguide elements 10 through the plurality of phase shifters 80, or 80a and 80b, the direction of the receivable light can be changed two-dimensionally.

For example, a light receiving device in which the light source 130 in the light scanning device 100 shown in fig. 12 is replaced with a receiving circuit can be configured. If light of wavelength λ is incident on the waveguide array 10A, the light is transmitted to the beam splitter 90 through the phase shifter array 80A, and finally concentrated at one location, and transmitted to the receiving circuit. The intensity of the light concentrated at the one portion can be said to represent the sensitivity of the light receiving device. The sensitivity of the light receiving device can be adjusted by adjusting elements assembled to the waveguide array and the phase shifter array 80A, respectively. In the light receiving device, for example, in fig. 4, the directions of wave number vectors (thick arrows in the drawing) become opposite. The incident light has a light component in a direction in which the waveguide element 10 extends (X direction in the drawing) and a light component in an arrangement direction of the waveguide element 10 (Y direction in the drawing). The sensitivity of the light component in the X-direction can be adjusted by an adjusting element assembled to the waveguide array 10A. On the other hand, the sensitivity of the light component in the arrangement direction of the waveguide element 10 can be adjusted by an adjusting element assembled to the phase shifter array 80A. Based on the phase difference Deltaphi of light when the sensitivity of the light receiving device is maximized, the refractive index n of the optical waveguide layer 20 _w And thickness d, can be known as θ and α shown in FIG. 4 ₀ . Therefore, the incident direction of light can be determined.

The above embodiments may be appropriately combined.

Finally, the above-described optical devices are summarized as the following items.

The optical device according to item 1 includes: a 1 st waveguide extending in the 1 st direction; and a 2 nd waveguide connected to the 1 st waveguide; the 2 nd waveguide includes: a 1 st mirror having a 1 st reflecting surface; a 2 nd mirror having a 2 nd reflecting surface facing the 1 st reflecting surface; and an optical waveguide layer between the 1 st mirror and the 2 nd mirror, the optical waveguide layer including a portion including a tip portion of the 1 st waveguide. At least one of the 1 st waveguide and the 2 nd waveguide has 1 or more gratings in a part of a connection region where the 1 st mirror, the 2 nd mirror, and the 1 st waveguide overlap when viewed from a direction perpendicular to the 1 st reflection surface. The 1 or more gratings are spaced apart from the end of the 1 st mirror or the 2 nd mirror in the connection region by a distance longer than at least one of the thickness of the 1 st mirror and the thickness of the 2 nd mirror in the 1 st direction.

In this optical device, even if the inclined portion is formed at the end portion on the side closer to the connection region of the 1 st mirror and/or the 2 nd mirror, light propagating in the 1 st waveguide can be efficiently coupled to the 2 nd waveguide via the grating without being affected by the inclined portion.

The optical device according to item 2 is the optical device according to item 1, wherein the connection region includes a 1 st region from the end portion to the 1 st or more gratings and a 2 nd region where the 1 st or more gratings are located. The sum of the length of the 1 st region in the 1 st direction and the length of the 2 nd region in the 1 st direction is shorter than one of the shorter half of the length of the 1 st mirror in the 1 st direction and the shorter half of the length of the 2 nd mirror in the 1 st direction.

In this optical device, it is possible to suppress the influence of defects and/or particles generated inside the optical waveguide layer on the optical coupling from the 1 st waveguide to the 2 nd waveguide.

The optical device according to item 3 is the optical device according to item 1 or 2, wherein a distance from the end portion to the 1 or more gratings is longer than a distance required for attenuation of the intensity of light propagating in the 1 st direction in the 2 nd waveguide by 1/e (e is a base of natural logarithm).

In the optical device, when light propagating in the 1 st waveguide is not coupled with the 2 nd waveguide via the grating, a part of the light propagates in the direction from the 2 nd waveguide toward the 1 st waveguide in the optical waveguide layer in the connection region. As a result, a part of the light is emitted rearward from the 1 st mirror and/or the 2 nd mirror.

The optical device according to item 4 is the optical device according to any one of items 1 to 3, wherein the transmittance of the 1 st mirror is higher than the transmittance of the 2 nd mirror. A part of the light inputted from the 1 st waveguide to the 2 nd waveguide in the optical waveguide layer is emitted via the 1 st mirror.

In the optical device, light is emitted via the 1 st mirror.

The optical device according to item 5 in the optical device according to any one of items 1 to 4, wherein the effective refractive index of the waveguide mode of the light propagating in the 1 st waveguide is n _e1 When the wavelength of the light in the air is lambda, the period of each of the 1 or more gratings is greater than lambda/n _e1 Less than lambda/(n) _e1 －1)。

In this optical device, by appropriately setting the period of the grating, light propagating in the 1 st waveguide can be coupled with high efficiency via the grating and the 2 nd waveguide.

Industrial applicability

The optical scanning device and the optical receiving device according to the present invention can be used for applications such as a lidar system mounted in a vehicle such as an automobile, a UAV, or an AGV.

Description of the reference numerals

10. Waveguide element and optical waveguide

11. Optical waveguide

10A waveguide array

15. 15a, 15b, 15c, 15m grating

20. Optical waveguide layer

30. 1 st mirror

40. 2 nd mirror

51. Dielectric layer

62A, 62B, 62A, 62B electrodes

73. Multiple partition walls

80. Phase shifter

80A phase shifter array

90. Light splitter

100. Optical scanning device

111. Connection region

112. Non-connection region

110. Driving circuit of waveguide array

130. Light source

210. Driving circuit of phase shifter array

310. Beam spot

400. Photodetector

500. Control circuit

600. A signal processing circuit.

Claims

1. An optical device, comprising:

a 1 st waveguide extending in the 1 st direction; and

a 2 nd waveguide extending in the 1 st direction;

the 2 nd waveguide includes:

a 1 st mirror having a 1 st reflecting surface;

a 2 nd mirror having a 2 nd reflecting surface facing the 1 st reflecting surface; and

an optical waveguide layer between the 1 st mirror and the 2 nd mirror;

at least one of the 1 st waveguide and the 2 nd waveguide has 1 or more gratings in a part of a region where the 1 st mirror, the 2 nd mirror, and the 1 st waveguide overlap when viewed from a direction perpendicular to the 1 st reflection surface;

the 1 or more gratings are spaced apart from the end of the 1 st mirror or the 2 nd mirror in the overlapping region by a distance longer than at least one of the thickness of the 1 st mirror and the thickness of the 2 nd mirror in the 1 st direction.

2. The optical device of claim 1, wherein,

the overlapped region includes a 1 st region from the end to the 1 st or more gratings and a 2 nd region where the 1 st or more gratings are located;

the sum of the length of the 1 st region in the 1 st direction and the length of the 2 nd region in the 1 st direction is shorter than one of the shorter half of the length of the 1 st mirror in the 1 st direction and the shorter half of the length of the 2 nd mirror in the 1 st direction.

3. The optical device according to claim 1 or 2, wherein,

the distance from the end to the 1 or more gratings is longer than the distance required for the attenuation of the intensity of the light propagating in the 1 st direction in the 2 nd waveguide to be 1/e times, and e is the bottom of the natural logarithm.

4. The optical device according to claim 1 to 3, wherein,

the transmittance of the 1 st mirror is higher than the transmittance of the 2 nd mirror;

a part of the light inputted from the 1 st waveguide to the 2 nd waveguide in the optical waveguide layer is emitted via the 1 st mirror.

5. The optical device according to any one of claims 1 to 4, wherein,

when the effective refractive index of the waveguide mode of the light propagating in the 1 st waveguide is n _e1 When the wavelength in the air of the light is lambda,

the period of each of the above 1 or more gratings is greater than lambda/n _e1 Less than lambda/(n) _e1 －1)。